Conductive polymer is widely being used for antistatic and electromagnetic wave-shielding coating layer, fuel cell, transparent electrode and so on. Particularly in the field of antistatic coating layer on the exterior glass of display device like CRT, LCD, PDP, transport tray for semiconductor device, LDC polarizer protective film, backlight unit protective film and so on, the conductive polymer becomes commercially used rapidly. Recently, as flat display devices are magnified, conductive coating layer, which can prevent goods from being damaged by static electricity as well as prevent from scratch and dust, becomes important. For example, the static electricity occurs because of a film adhesion in the step of removing protective film during the production of large LCD substrate, which may result in a fatal damage.
As conductive components of the antistatic coating layer, metal(aluminum, etc.), carbon black, non-conductive polymer containing conductive additives (surfactant which has ion conductivity when it reacts with moisture) and conductive polymer(polythiophene, polypyrrole, polyaniline, which themselves have conductivity) are known. As the surfactant, a quaternary ammonium divalent salt type surfactant was used, but it had a limit for LCD protective film of high quality TFT because of the low antistatic function. Also, the conventional conductive polymer is not easy to be mass-produced, and has disadvantages of low solubility, light permeability, thermal stability and external stability. Polyethylene dioxythiophene(PEDT), a conductive polymer which overcame the above mentioned disadvantages to improve processing property, light permeability and moisture-resistance, was developed by Bayer (U.S. Pat. No. 5,035,926). In addition, Baytron P and Baytron P H, which are PEDT doped with polystyrene sulfonic acid(a polymer acid), are placed on the market. However, PEDT(Baytron P, Baytron PHI, etc.) itself is an aqueous-dispersed solution, consequently, has a limit for coating property such as adhesion to the substrate(polymer film, glass etc.), strength of layer and drying property.
Generally, the conductive coating layer is formed by coating a coating composition which includes conductive polymer, water-soluble or alkali-soluble binder and volatile solvent(alcohol, etc.) on a substrate(thing to be coated, glass, polymer film, etc.); and drying at a certain temperature. As an example of the coating composition, an antistatic coating composition was disclosed, which included Baytron P as the conductive polymer and self-emulsifying polyester resin aqueous-dispersed solution (Korean Patent Publication No. 2002-0016549, Japanese Patent Publication No. 2005-281704). The surface resistance of coating layer formed with the coating composition was initially 105˜6 Ω/□, and it increased sharply after 10 days to 1012Ω/□, consequently, the antistatic function becomes inferior as time passes. This aging property is so inferior that the initial low surfaces resistance is meaningless, and there is a problem with applying it to high quality and large LCD.